Attention is paid to development of an EL display using an electroluminescence (Electro Luminescence; hereinafter, abbreviated to “EL”) element that is a light-emitting element that has characteristics such as self-light emission, wide viewing angle, high-speed response, low voltage drive, and low power consumption.
An EL display is classified into a passive matrix type or an active matrix type depending on a driving method of an EL element.
In an active matrix EL display, a thin film transistor (Thin Film Transistor; hereinafter, abbreviated to “TFT”) is used for driving an EL element, and generally, after forming on a substrate a driver circuit comprising a TFT, and the like, an EL element is further formed thereover.
As an active matrix EL display, for example, a display that has a structure of an anode provided on a planarizing insulating film and a source electrode of a TFT connected to the anode of an organic EL element through a contact hole provided in the planarizing insulating film has been proposed (see Patent Document 1, for example).
As a method of forming a planarizing insulating film, a method of forming a film that has self-planarization such as an organic resin film for planarization can be given as a quite simple method.
However, many of films that have self-planarization such as an organic resin film have low heat resistance. In addition, there is fear that gas is generated from the film after forming the film to cause degradation of an EL element since the film includes a volatile solvent. It is generally possible to suppress such degradation of an EL element due to gas generated from the film by performing appropriate treatment.
On the other hand, instead of the organic resin film mentioned above, an inorganic insulating film with high heat resistance from which gas is unlikely to be generated may be used for fear of generation of gas.
However, it is often the case that many of insulating films from which no gas is generated have no self-planarization. Therefore, a step generated due to a difference between laminated structures forming respective portions on a TFT array substrate is reflected with the result that the insulating film has an uneven surface. In the case of forming an electrode of an EL element on the uneven insulating film, electric field becomes concentrated at an edge, which can cause acceleration of degradation of the EL element. In addition, unevenness generated due to surface roughness generated on the insulating film cannot be completely covered with a light-emitting layer with the result that an anode and a cathode of a light-emitting element sometimes short out. Therefore, measures such as planarization of an interlayer insulating film by CMP (Chemical Mechanical Polishing) or the like is applied.
Patent Document 1: Japanese Patent Laid-Open 2000-77191 (pages 2 to 4, FIG. 1).